This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
The results of calling set priorirty on a thread will depend on how the operating system handles threads and priorities and also on other threads that are alive at any given point in time. Let us say you have only one thread running, you can reduce it's priority all the way to min_priority and it will still continue to run. Let us say you are running on an OS that implements preemptive scheduling and the current thread is set at priority 5, Let us also say that all other threads that are ready to run are at min_priority. If you reduce the priority of the current thread to 3, it will still continue to run. You can not predict/guarantee the results of setting priority on a thread. Hope this helps